﻿// Spun AJAX Framework
// Copyright (C) 2008 Blake Hegerle
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Formality.FormalSystem
{
    public abstract class Proposition : Sentence
    {
        public override Inference? Implies(Proposition that, IEnumerable<Sentence> Given)
        {
            var thatProp = that as Proposition;

            if (thatProp == null)
                return null;

            var Sub = new Substitution();

            var Inference = Matches(thatProp, Sub);

            if (Inference.HasValue)
            {
                Inference = new Inference
                {
                    Antecedents = new Sentence[] { this },
                    Description = string.Format("{0} {1}", DisplayId, Sub.ToString())
                };
            }

            return Inference;
        }

        public abstract Inference? Matches(Proposition that, Substitution Substitution);
        public abstract Proposition Replace(Substitution Substitution);

        public virtual IEnumerable<Proposition> ApplyTemplate(Proposition Template, Proposition Replacement)
        {
            var Sub = new Substitution();

            if (Template.Matches(this, Sub).HasValue)
                yield return Replacement.Replace(Sub);
        }
    }
}
